No GPS Until Activated: if turned "ON" Gaia GPS will not locate you or track your movements until you engage the GPS with the Location crosshairs or start a track recording

Collapse the compass band: The app will not use location services to find your compass direction

Apple has a useful site that lists ways to preserve battery life. Additionally, Adventure Alan has a very informative website that explains how to use the iPhone as a GPS tracking device, including detailed information on reducing battery loss.